11:15 AM - 11:30 AM
[ACG38-03] Dynamics of the estern-boundary currents
★Invited Papers
Keywords:coastal trapped waves, planetary Rossby waves, eastern boundary currents, baroclinic flow
This presentation is mostly a review of the eastern boundary structure with emphasis on the Leeuwin Current System along the west coast of Australia. Some preliminary descriptive results will also be shown about the annual variability of LCS.
Baroclinic coastal Kelvin waves propagate poleward along the eastern boundary of the ocean basin. If there is some forcing along the coast or a flow into or out of the eastern boundary, such as Ekman drift, pressure anomaly is generated and is propagated by the coastal Kelvin wave. This process establishes a coastal current in the wake of the wave.
Equatorward of the critical latitude, however, pressure anomaly along the eastern boundary is carried away offshore by Rossby waves. For this reason, for a narrow current to exist along the eastern boundary, some mechanism is necessary to arrest the propagation of Rossby waves. One potentially powerful mechanism is the bottom slope (topographic beta). The Leeuwin Current (LC), a shallow, permanent, poleward-flowing eastern boundary current anchored to the shelf break, owes its existence to the bottom slope.
There is a permanent undercurrent flowing equatorward hugging the continental slope beneath the LC. The mechanism of its generation is a mystery. Qualitatively the pair of the LC and the undercurrent looks like a baroclinic mode of the coastal trapped wave. Can such a mode, however, remain trapped against the Rossby waves? If it can, what is the forcing?
There is also variability at various time scales. It is not known whether or not baroclinic variability due to the various modes of coastal trapped waves can remain trapped to the eastern boundary. There have been reports that during its normal annual cycle, the LC sheds eddies when it is strong. This may be a mechanism for the LCS to lose energy into the interior.
The structure of the eastern-boundary current system is crucial to determine the baroclinic structure of the interior ocean as its structure propagates as Rossby waves.
Baroclinic coastal Kelvin waves propagate poleward along the eastern boundary of the ocean basin. If there is some forcing along the coast or a flow into or out of the eastern boundary, such as Ekman drift, pressure anomaly is generated and is propagated by the coastal Kelvin wave. This process establishes a coastal current in the wake of the wave.
Equatorward of the critical latitude, however, pressure anomaly along the eastern boundary is carried away offshore by Rossby waves. For this reason, for a narrow current to exist along the eastern boundary, some mechanism is necessary to arrest the propagation of Rossby waves. One potentially powerful mechanism is the bottom slope (topographic beta). The Leeuwin Current (LC), a shallow, permanent, poleward-flowing eastern boundary current anchored to the shelf break, owes its existence to the bottom slope.
There is a permanent undercurrent flowing equatorward hugging the continental slope beneath the LC. The mechanism of its generation is a mystery. Qualitatively the pair of the LC and the undercurrent looks like a baroclinic mode of the coastal trapped wave. Can such a mode, however, remain trapped against the Rossby waves? If it can, what is the forcing?
There is also variability at various time scales. It is not known whether or not baroclinic variability due to the various modes of coastal trapped waves can remain trapped to the eastern boundary. There have been reports that during its normal annual cycle, the LC sheds eddies when it is strong. This may be a mechanism for the LCS to lose energy into the interior.
The structure of the eastern-boundary current system is crucial to determine the baroclinic structure of the interior ocean as its structure propagates as Rossby waves.